The rapid adjustments in length, tension and position of the vocal folds which occur during phonation, suggests a finely coordinated reflex system. This study is designed to test the HYPOTHESIS that adjustments of finely coordinated reflex systems occur because the central nervous system (CNS) receives sensory cues from laryngeal receptors activated during phonation. The approach is aimed at understanding laryngeal sensory processing. It is not known what sensory signals arise within the larynx during phonation; nor is it known how this information is used by the CNS to control vocal performance. Diseases in humans which may occur as a result of aberrations in the system to be investigated include the aging voice, spasmotic dysphonia, essential voice tremor, myasthenia laryngis, and certain chronic cough conditions. Continued research in laryngeal neurophysiology will be necessary before such diseases are better understood. Classifications of laryngeal mechanoreceptors have been reported, based on the types of stimuli applied to the larynx. Touch, pressure, muscle stretch, vibration, joint movement, and airflow have been used to stimulate the larynx during afferent nerve recording. However, afferent activity from the larynx has not been measured during phonation. During preliminary work, vocalizations were evoked in anesthetized cats by electrical stimulation of midbrain periaqueductal gray. Single-unit recordings were made from the superior laryngeal nerve during vocalization. It is clear that phonation specific impulses do travel in the internal branch of the superior laryngeal nerve during phonation. Four types of afferent activity have been seen: 1) frequency following during phonation, 20 expiratory, 30 inspiratory, 4) sensitive to touching the epiglottis. These results suggest that this model can be used to study mechanoreceptor activity during phonation. The SPECIFIC AIMS are to a) determine what phonation-specific cues travel in laryngeal nerves during phonation, and b) to compare and contrast the types of sensory information carried during phonation by the internal branch of the superior laryngeal nerve (all sensory fibers) with those carried by the external branch of the superior laryngeal and the recurrent laryngeal nerves (both are motor nerves that contain some sensory fibers). Obtaining these data is a necessary first step to determine what information is available to primary relay stations and integrating areas in the brainstem during phonation.